The present invention concerns pharmaceutical compositions containing human epidermal growth factor (EGF) and methods for making and using such compositions. In particular, the invention relates to such pharmaceutical compositions having increased stability as a result of being combined with a metal cation, such as zinc.
Human EGF (also known as urogastrone) is a 53 amino acid polypeptide growth factor that has mitogenic activity for a number of kinds of cells, including epithelial and mesenchymal cells. Variants of the human EGF polypeptide have been reported, such as the 52 amino acid gamma-urogastrone. EGF has been reported to be useful in increasing the rate of wound healing as a result of its mitogenic effect. EGF has also been reported as being useful for treating gastric ulcers. A review of EGF is provided by Carpenter et al., in "Epidermal Growth Factor, Its Receptor and Related Proteins," Experimental Cell Research, 164:1-10 (1986).
An important objective in the therapeutic use of EGF is the development of a stable pharmaceutical EGF formulation that has a long shelf life and is capable of remaining as a predominantly active single species of EGF over a long period of time. However, because of the inherent instability of EGF, difficulties have been encountered in developing such a stable EGF formulation. For instance, EGF loses biological activity in the presence of moisture. U.S. Pat. No. 4,717,717 describes compositions and methods for stabilizing EGF against such a loss of biological activity. Also, human EGF loses activity over time and produces multiple species of the EGF molecule, which have been identified by high performance liquid chromatography (HPLC). These multiple species of EGF are believed to be breakdown products resulting from the degradation of EGF or derivatives resulting from the chemical modification of EGF. It is believed that there are at least three such degradation products, some or all of which have reduced EGF biological activity. Incubation of EGF at 45.degree. C. accelerates the formation of the degradation products normally found with long term storage at ambient temperature. Such degradation, and the associated loss of biological activity of EGF, is a disadvantage because it makes it impractical to store aqueous or solid preparations of EGF over extended periods of time.
The present invention provides a means for reducing the degradation of the EGF molecule and the resulting loss of biological activity.